Relapse to cocaine use, the highest among commonly abused illicit drugs, is a serious public problem and represents the primary challenge that exists for the treatment of cocaine addicts. Despite extensive investigation, molecular substrates that can serve as potential therapeutic targets to prevent relapse are limited. Thus, understanding the mechanisms of relapse and identifying new molecular targets for developing pharmacological treatments will greatly aid the field of addiction research. Recent preclinical rodent studies have suggested that craving and drug-induced relapse is mediated by enhanced synaptic AMPAR transmission in the nucleus accumbens (NAc) via GluA2-lacking-, GluA1-containinng-Ca2+-permeable AMPA receptors (CP-AMPARs). Work from our laboratory has identified the Cav1.2 L-type Ca2+ channel (LTCC) as a promising candidate for mediating cocaine-induced long-term behavioral responses and in regulating cell surface AMPARs. Using psychomotor sensitization, we find that Cav1.2 channels in the NAc, mediates cocaine-induced expression of sensitization following extended periods of withdrawal. Using the reinstatement of cocaine CPP model, we find that the LTCC antagonist, diltiazem delivered directly into the NAc blocks cocaine-induced reinstatement of cocaine CPP. Furthermore, we have found that Cav1.2-activated kinase pathways (CaMKII and ERK) regulate cocaine-induced increase in cell surface GluA1, but not GluA2 in the NAc. Thus, in this RO1 application we aim to capitalize on the knowledge we have gained to further explore molecular targets that mediate relapse to cocaine. We will test the central hypothesis that Cav1.2- activated kinase pathways in the NAc mediate cocaine-induced reinstatement of cocaine seeking via increase in NAc synaptic CP-AMPARs. To circumvent the challenge of the lack of Cav1.2-specific blockers, we propose to use the cutting edge Cre-lox P technology to generate local Cav1.2 knockout in the mouse NAc. Kinases will be manipulated by the use of viral vectors. In Aim 1.1, adenoassociated viral (AAV) vectors expressing Cre recombinase will be stereotaxically delivered into the NAc of Cav1.2 floxed mice. Mice will be behaviorally tested in cocaine-induced reinstatement of cocaine CPP. In Aim 1.2, molecular studies will be pursued to examine Cav1.2-induced AMPAR trafficking. In Aim 1.3, electron microscopy will be utilized to examine GluA1 trafficking in dopamine D1 neurons in the NAc shell. In Aim 2.1, viral vectors expressing kinase inhibitors will be stereotaxically delivered into the NAc of C57BL/6 mice. Mice will be behaviorally tested in cocaine-induced reinstatement of cocaine CPP. In Aim 2.2, role of kinases in AMPAR trafficking will be examined. In Aim 3, the functional significance of NAc CP-AMPARs, GluA1 trafficking and GluA1 phosphorylation in cocaine-induced reinstatement will be examined using pharmacology and genetic mutant mice. The results obtained from this study could greatly advance the field of cocaine addiction by identifying discrete molecular targets for developing pharmacological treatments for cocaine addicts.